Mechanical wet air generators, or wet N.sub.2 generators have been used in the chemical processing industry for providing wet air or wet N.sub.2. Normally, a clean dry air (CDA) or a N.sub.2 gas contains between about 20% and about 30% RH (relative humidity) which is not suitable for many chemical processes wherein a wet air blanket or a wet N.sub.2 blanket is necessary.
For instance, in a slurry supply tank used for an oxide slurry supply system for chemical mechanical polishing, a wet N.sub.2 blanket must be used to shield the slurry solution from dry air and to dispense the slurry without drying the slurry particles. When the N.sub.2 gas used has a low water content, i.e., at 20.about.30% RH, some of the slurry particles tend to dry up and adhere to other particles and forms particles in forming particles of significantly larger size. This presents a serious scratching problem when the slurry solution is subsequently dispensed on a wafer surface for polishing. In a normal slurry solution, the composition ratio between solids and water is approximately 1:1. When the nitrogen blanket or the clean dry air blanket covering the slurry solution contains less than 30% RH, the water content in the slurry may further vaporize and thus causing the formation of larger particles. The use of a wet N.sub.2, or a wet CDA blanket over a slurry solution is therefore an important processing step that must be carried out in order to assure the reliability of the CMA process.
Conventionally, wet air or wet N.sub.2 is provided by a wet air generator or a wet N.sub.2 generator such as that shown in FIGS. 1 and 2. FIG. 1 shows a wet N.sub.2 generator 10 constructed of three wet N.sub.2 generation chambers 12. In each of the generation chamber, a gas/water inlet 14 is provided at the bottom of the chamber. A mixture of N.sub.2 gas and water is pumped into inlet 14 through a flow control apparatus 20. Each of the wet N.sub.2 generator 12, also shown in FIG. 2, is filled with a filter-type material for retaining water and for maximizing the contact area with nitrogen gas that is fed therethrough. The wet N.sub.2 generator chambers 12 are further equipped with heating means (not shown) such that water may be heated inside the chamber to further increase the humidity content of N.sub.2 gas purged therethrough. The water level in each of the generator chamber 12 is controlled by level sensors "H" for high level detection and "L" for low level detection. These are shown in FIG. 1 as 22 for the high level sensor and 24 for the low level sensor. The nitrogen gas which carries moisture then exits the wet N.sub.2 outlet 28 mounted at the top of each of the wet N.sub.2 generator chamber 12.
The conventional wet N.sub.2 generator shown in FIGS. 1 and 2, even though widely used, presents many processing disadvantages. First, large bubble formation in the wet N.sub.2 generator chambers frequently causes the malfunction of the water level sensors. The malfunction causes the level sensors to be turned on and off constantly and furthermore, causes water to overflow into a slurry piping. The constant turn on and off of the level sensors further necessities frequent adjustments and maintenance procedures to be performed. Moreover, the conventional wet N.sub.2 generator chambers are not equipped with protection devices for preventing overflow of water into the slurry piping which dilutes the slurry solution, decreases its concentration and thus makes the process control of the CMP process very difficult. The conventional wet N.sub.2 generator chambers are not equipped with means for removing over-saturated water contained in wet N.sub.2. The large bubbles produced further reduces the wetting effect of water such that a higher heating temperature of water is equipped leading to a more difficult to control process.
It is therefore an object of the present invention to provide a mechanical wet air generator does not have the drawbacks or shortcomings of the conventional generators.
It is another object of the present invention to provide a mechanical wet air generator that is equipped with an inner container formed of perforated panels situated inside an outer container of fluid-tight construction for establishing fluid communication with an inner cavity of the inner container.
It is a further object of the present invention to provide a mechanical wet air generator that is capable of producing either wet air or wet N.sub.2.
It is another further object of the present invention to provide a mechanical wet air generator that is equipped with a reliable fluid level controller for controlling the fluid level in the generator such that an overflow of fluid into a slurry pipe is prevented.
It is still another object of the present invention to provide a mechanical wet air generator that is equipped with an inner container filled with a multiplicity of bubble-breaking solid shapes for preventing the formation of large bubbles.
It is yet another object of the present invention to provide a mechanical wet air generator which is capable of producing wet air or wet N.sub.2 that contains at least 90% relative humidity.
It is still another further object of the present invention to provide a mechanical wet air generator that is further equipped with a demister in series connected and downstream to the wet air generator for separating over-saturated water from the wet air.
It is yet another further object of the present invention to provide a mechanical wet air generator that is equipped with an inner container further includes a heater and a thermocouple for controlling a temperature of the fluid contained in the cavity of the inner container.